Warmest, most breathable winter mid layer

By far, the most common layer I wore last winter in NH was the Polartec Power Dry HE. I've got Patagonia Cap 4 versions and Marmot Thermo versions (basically the same). Bottoms, tops, beanie, and balaclava. The stuff is awesome. Warm when it needs to be, breathable when to accomodate activity or warmer temps.

On a 30 degree day, I'll wear it as the only layer (next to my skin). On cold days, I'll wear it as a mid layer over a thin tech T of some kind.

If it's cold and windy, I'll throw a wind breaker of some sort on top. When I stop, I'll put on a down hoody.

Stuff is fantastic. I've worn it on 11 degree (F) days. I've worn it as PJs camping with overnight lows in the 50s.

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If I need more warmth (crazy cold or for just sitting around), Power Stretch fleece (or the R1 version). On a budget? 100 wt Polartec microfleece.

I'll second that – if I am right about what Power Dry HE is!

My patagonia Cap 4 is by far my most worn garment on the trail, and running in Chicago along the lakefront in January. During summer months if I'm going to any altitude I wear it to sleep in, then during shoulder seasons it's great for such a huge range in temps. No wind stop – nice and airy. wind break of some kind – super warm. Then add a base under it, and/or a heavier fleece/puffy on top and I can take this puppy down to the negative single digits.

My coldest run ever was a january run along Lake Michigan, -12!! and the cap 4 was my "insulating" layer. Very nice indeed (as nice as it can be to run on a windy lakefront in -12 degrees…but you get the idea)

Cap 4 and the various immitators, because it does the best job thermoregulating. My personal favorite apparel innovation in the past five years.

My go to mid layer when temps go below ~30, and my go to base layer between ~ the mid 40's and 30.

Dang it, i'll have to conform here, and put in another vote for the Polartec Power Dry High Efficiency stuff (say that 5 times fast) with a hood as a great and versatile midlayer.

I've also experimented with using polypropylene fishnet as a mid layer in conjunction with a windjacket and more traditional baselayer–that works pretty good too, though it seems to work better as a baselayer overall. I used it in conjunction with wool-poly blend baselayers with the idea of not stinking up the polypropylene as much.

Anyways, arguably the *most breathable* midlayer that money can buy hands down.

During future polar vortex events in winter, i plan on trying a COMBO of Cap 4 or MEC 3 Hoody with a Polypropylene fishnet (i hear people murmuring softly in disbelief, that's just too cray cray), a thin silk baselayer, and good windjacket.

Haven't figured out the order i want to try it in. Maybe Cap 4 hoody as baselayer, silk over same, then PP fishnet, then windjacket? Or maybe Cap 4, PP fishnet, thin silk, then windjacket? In either case, man, would really stink if yah ripped a large hole in the windjacket or the zipper stopped working though.

Polyester fleece–whatever I happen to find. It's generally either a discount store garment purchased for $20 or so, or one given to me free at work (logo wear).

If that isn't warm enough, I either add another or add a thicker polyester base layer.